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• What is the best way to "carve" a terrain created from a heightmap?

  - by tigrou

  I have a 3d landscape created from a heightmap. I'd like to "carve" some holes in that terrain. That will allow me to create bridges, caverns and tunnels inside it. That operation will be done in the game editor so it doesn't need to be realtime. In the end, rendering is done using traditional polygons. What would be the best/easiest way to do that ? I already think about several solutions : Solution 1 1) Create voxels from the heightmap (very easy). In other words, fill a 3D array like this : voxels[32][32][32] from the heightmap values. 2) Carve holes in the voxels as i want (easy too). 3) Convert voxels to polygons using some iso-surface extraction technique (like marching cubes). 4) Reduce (decimate) polygons created in 3). This technique seems to be the most promising for giving good results (untested). However the problem with marching cubes is that they tends to produce lots of polygons thus reducing them is mandatory. Implementing 4) also seems not trivial, i have read several papers on the web and it seems pretty complex. I was also unable to find an example, code snippet or something to start writing an algorithm for triangle mesh decimation. Maybe there is a special decimation algorithm (simpler) for meshes created from marching cubes ? Solution 2 1) Create some triangle mesh from the heighmap (easy). 2) Apply severals 3D boolean operation (eg: subtraction with a sphere) to carve the mesh. 3) apply some procedure to reduce polygons (optional). Operation 2) seems to be very complex and to be honest i have no idea how to do that. Also applying many boolean operation seems to be slow and will maybe degrade the triangle mesh every time a boolean operation is applied.

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• What is the best way to check if there is overlap between player and static, non-collidable items in bullet physic engine

  - by tigrou

  I'd like to add non collidable objects (eg: power ups, items, ...) in a game world using Bullet Physics Engine and to know if there is collision between player and them. Some info : there is a lot of items ( 1000), all are box shapes and they don't overlap. Here is things i have tried : btDbvt* bvtItems = new btDbvt(); //btDbvt is a hierachical AABB tree, used by Bullet foreach(var item ...) { btDbvtVolume volume = ... //compute item AABB; bvtItems->insert(volume, (void*)someExtraData); } Then, to find collisions between items and player : playerRigidBody->getAabb(min, max); btDbvtVolume playervolume = ... //compute player AABB bvtItems->collideTV(bvtItems->m_root, playervolume, *someCollisionHandler); This works fairly well (and its very fast), however, there is a problem : it only check items AABB against player AABB. That loss of precision is acceptable for items but not for player which is not a box. It would actually need another check to make sure player really collide with item but i don't know how to do this in Bullet. It would have been nice to have a function like this : playerRigidBody->checkCollisionWithAABB(); After doing trying that, I discovered that a btGhostObject exist and seems to have been made for that. I changed my code like this : foreach(var item...) { btCollisionObject* ghostObject = new btGhostObject(); ghostObject->setCollisionShape(boxShape); ghostObject->setCollisionFlags(ghostObject->getCollisionFlags() | btCollisionObject::CF_NO_CONTACT_RESPONSE); startTransform.setOrigin(...); //item position ghostObject->setWorldTransform(startTransform); dynamicsWorld->addCollisionObject(ghostObject, btBroadphaseProxy::SensorTrigger, btBroadphaseProxy:: CharacterFilter); } It also works ok, but there is a huge fps drop (almost ten times slower) which is not acceptable. Maybe there is something missing (forget set a flag) and Bullet is doing extra job for nothing or maybe all that ghostObjects are polluting broad phase and ghostObject is not the right thing for that. Any help would be appreciated.

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• What is the best way to implement collision detection using Bullet physics engine and a track generated from a curve?

  - by tigrou

  I am developing a small racing game were the track is generated from a curve. As said above, the track is generated, but not infinite. The track of one level could fit with no problem in memory and will contain a reasonably small amount of triangles. For collisions, I would like to use Bullet physics engine and know what is the best way to handle collisions with the track efficiently. NOTE : The track will be stored as a static rigid body (mass = 0). The player will be represented by a sphere shape for collisions. Here is some possibilities i have in mind : Create one rigid body, then, put all triangles of the track (except non collidable stuff) into it. Result : 1 body with many triangles (eg : 30000 triangles) Split the track into several sections (eg: 10 sections). Then, for each section, create a rigid body and put corresponding triangles in it. Result : small amount of bodies with relatively small amount of triangles (eg : 1500 triangles per section). Split the track into many sub-sections (eg : 1200 sections). Here one subsection = very small step when generating the curve. Again for each sub-section, create a body and put triangles in it. Result : many bodies with very small amount of triangles (eg : 20 triangles). Advantage : it could be possible to "extra data" to each of the subsection, that could be used when handling collisions. Same as 2, but only put sections N and N+1 in physics engine (where N = current section where the player is). When player reach section N+1, unload section N and load section N+2 and so on... Issue : harder to implement, problems if the player suddenly "jump" from one section to another (eg : player fly away from section N, and fall on section N + 4 that was underneath : no collision handled, player will fall into void ) Same as 4, but with many sub-sections. Issues : since subsections are very small there will be constantly new bodies added and removed to physics engine at runtime. Possibilities for player to accidently skip some sections and fall into the void are higher than 4.

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• Problem when texturing triangles using glVertexPointer()

  - by tigrou

  I'm having a problem for displaying a single quad, here is how i do : float tex_coord[] = { 0.0, 0.0, 0.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 0.0, 0.0, 0.0 }; //how many coords should i give ? int indexes[] = { 3, 2, 0, 0, 1, 3 } float vertexes[] = { -37, 0, 30, -38, 0, 29, -41, 0, 32, -42, 0, 31 } glEnableClientState(GL_TEXTURE_COORD_ARRAY); glEnableClientState(GL_VERTEX_ARRAY); glVertexPointer(3, GL_FLOAT, 0, vertexes); glTexCoordPointer(2, GL_FLOAT, 0, tex_coord); glDrawElements(GL_TRIANGLES, 2, GL_UNSIGNED_INT, indices); glDisableClientState(GL_VERTEX_ARRAY); glDisableClientState(GL_TEXTURE_COORD_ARRAY); The result : (with 2 triangles) (with 4 triangles)

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• Is using a dedicated thread just for sending gpu commands a good idea?

  - by tigrou

  The most basic game loop is like this : while(1) { update(); draw(); swapbuffers(); } This is very simple but have a problem : some drawing commands can be blocking and cpu will wait while he could do other things (like processing next update() call). Another possible solution i have in mind would be to use two threads : one for updating and preparing commands to be sent to gpu, and one for sending these commands to the gpu : //first thread while(1) { update(); render(); // use gamestate to generate all needed triangles and commands for gpu // put them in a buffer, no command is send to gpu // two buffers will be used, see below pulse(); //signal the other thread data is ready } //second thread while(1) { wait(); // wait for second thread for data to come send_data_togpu(); // send prepared commands from buffer to graphic card swapbuffers(); } also : two buffers would be used, so one buffer could be filled with gpu commands while the other would be processed by gpu. Do you thing such a solution would be effective ? What would be advantages and disadvantages of such a solution (especially against a simpler solution (eg : single threaded with triple buffering enabled) ?

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• Is this JS code a good way for defining class with private methods?

  - by tigrou

  I was recently browsing a open source JavaScript project. The project is a straight port from another project in C language. It mostly use static methods, packed together in classes. Most classes are implemented using this pattern : Foo = (function () { var privateField = "bar"; var publicField = "bar";     function publicMethod() { console.log('this is public');     } function privateMethod() { console.log('this is private'); } return {   publicMethod : publicMethod, publicField : publicField }; })(); This was the first time I saw private methods implemented that way. I perfectly understand how it works, using a anonymous method. Here is my question : is this pattern a good practice ? What are the actual limitations or caveats ? Usually i declare my JavaScript classes like that : Foo = new function () { var privateField = "test"; this.publicField = "test";     this.publicMethod = function()     { console.log('this method is public'); privateMethod();     } function privateMethod() { console.log('this method is private'); } }; Other than syntax, is there any difference with the pattern show above ?

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• How to convert JPEG JFIF files to JPEG Exif format?

  - by tigrou

  I recently put the SD card of my camera in a Windows 7 PC and start browsing pictures on it. I noticed some were not aligned correctly and use rotate feature included in Windows Photo Viewer in order to view them as I wanted. What I didn't know is that when rotate feature is used, it also overwrite the picture when pressing next or previous button resulting in a possible loss of quality (which is in my opinion a bad idea, app should at least warn user of what will happened when using such a feature). After that, I re-inserted the SD card back in my camera and bad surprise happened : the rotated picture could not be previewed anymore. Instead, i got a black screen saying "Incompatible JPEG format". Other files (untouched) are still working ok. To try to understand what happened I opened a JPEG file from camera and one generated on windows 7 in a hex editor. Here is the difference : The camera JPEG files have a Exif tag in them (with 0xE1 in header). Other JPEG files (Windows 7) have first a JFIF tag in it, followed by a Exif tag (with 0xE0 in header). So if i understand it well, both are JPEG files, but using a different internal format. Here is my question : is it possible (using some tool) to convert JFIF files to Exif format ? I understand that original camera files have been reencoded and thus lose some quality (getting originals back is impossible). What i want know if convert them from JFIF back to Exif (without a second loss of quality if possible...)

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• How is it possible for SSD's drives to have such a good latency?

  - by tigrou

  First time i read some information about SSD's, i was surprised to learn they internally use NAND flash chips. This kind of memory is generally slow (low bandwidth) and have high latency while SSD's are just the opposite. But here is how it works : SSD drives increase their bandwidth by using several NAND flash chips in parallel. In other words, they do some data striping (aka RAID0) across several chips (done by the controller). What i don't understand is how SSD's drives have such a low latency, whereas they are using NAND chips? (or at least lot better than what a typical single NAND chip would do) EDIT: I think under-estimate NAND chip capabilities. USB drives, while powered by NAND's are mostly limited by USB protocol (which have a pretty high latency) and the USB controller. That explain their poor performance in some cases.

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• How to know what dll or services taskhost.exe is hosting?

  - by tigrou

  I have recently discover a new process in the task manager : taskhost.exe (maybe it was there before but i did not notice it) As the name implies, it seems to be used for running dll in background (like rundll32.exe). Is there a way to know which dll / services this process is hosting ? i would like to know for which purpose it is used and if there is some malware or not. I know it is possible to see which services svchost.exe process is hosting using process explorer utility. I have checked taskhost.exe threads and their stacks using process explorer, here is what i get : So it seems it is used for sound (winmm + playsndsrv). But there is also other things for which very few information is provided (ex : thread 1456, taskhost.exe as start address and nothing relevant can be found in stack (same for 1464, 2272 and so). So maybe it is not the right way to do.

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• How SSD's drives reduce their latency?

  - by tigrou

  First time i read some information about SSD's, i was surprised to learn they internally use NAND flash chips. This kind of memory is generally slow (low bandwidth) and have high latency while SSD's are just the opposite. But here is how it works : SSD drives increase their bandwidth by using several NAND flash chips in parallel. In other words, they do some data striping (aka RAID0) across several chips (done by the controller). What i don't understand is how SSD's drives managed to reduce latency? (or at least lot better than what a single NAND chip without any controller can do)

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• In Windows 7, is there a way to know how much memory a service is using?

  - by tigrou

  In windows 7, is there a way (by using common interface or a custom utility) to know how much memory a specific windows service is using ? It seems most services are hosted by svchost.exe processes ( some svchosts.exe processes seems to host tons of services). While it is possible to know which services are hosted by a specific process, I found no way to get information about how much memory a service take.

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• How SqlDataAdapter works internally?

  - by tigrou

  I wonder how SqlDataAdapter works internally, especially when using UpdateCommand for updating a huge DataTable (since it's usually a lot faster that just sending sql statements from a loop). Here is some idea I have in mind : It creates a prepared sql statement (using SqlCommand.Prepare()) with CommandText filled and sql parameters initialized with correct sql types. Then, it loops on datarows that need to be updated, and for each record, it updates parameters values, and call SqlCommand.ExecuteNonQuery(). It creates a bunch of SqlCommand objects with everything filled inside (CommandText and sql parameters). Several SqlCommands at once are then batched to the server (depending of UpdateBatchSize). It uses some special, low level or undocumented sql driver instructions that allow to perform an update on several rows in a effecient way (rows to update would need to be provided using a special data format and a the same sql query (UpdateCommand here) would be executed against each of these rows).

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